Auto focusing while shooting stills is completely different than when shooting video. This can be a challenge for photographers whose only experience is shooting stills, as well as for experienced videographers who have little experience with HD-SLRs.

When shooting still pictures, the camera uses a sophisticated sensor that’s dedicated exclusively for autofocus operation. This “phase-detection” AF system can detect whether a subject is in or out of focus. More importantly, it can detect what direction to move the lens to get sharp focus; if the subject is moving; and how fast the subject is moving.

The phase detection AF system can quickly acquire focus and track moving subjects, but the mirror must be down for this system to operate. Therefore, you must view the scene through the eye-level finder when using the cameras primary autofocus system.